1. Field of the Invention
The present invention relates to a liquid circulation heating system for performing air-heating using a liquid.
2. Description of Related Art
Conventionally, there has been known a liquid circulation heating system for producing hot water by a boiler or an electric heater and performing air-heating using the hot water produced. In recent years, the use of a heat pump capable of producing hot water with high efficiency has been considered as an alternative heat source to a boiler and an electric heater. For example, JP 2008-39306 A proposes a liquid circulation heating system for producing hot water by a heat pump and storing the produced hot water in a hot water storage tank. In this liquid circulation heating system, the hot water stored in the hot water storage tank is fed to, for example, a heating radiator placed indoors to radiate its heat, and then returned to the hot water storage tank.
In the liquid circulation heating system having such a configuration, it is conceived that the power consumption of the heat pump is reduced by utilizing solar heat (which is obtained by converting solar energy into thermal energy) to produce hot water. For example, JP 2002-162109 A proposes a hot water supply system using a solar collector, although it is not a liquid circulation heating system. In this hot water supply system, a heat exchanger is provided at a lower position in a hot water storage tank. A heating medium is circulated through a circulation passage passing through the heat exchanger and the solar collector, so that the water in the hot water storage tank is heated by solar heat.